This post was authored by Joel Don, ISA's social media community manager.

This automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.

Which of the following will have the highest pressure difference between the surface and 6 inches below the surface?

a) a 12-in-vertical straw filled with water
b) a 10-ft-diameter open tank filled with water
c) a 5-ft-diameter vertical pipe filled with water
d) a 7-ft-diameter vertical pipe filled with water
e) none of the above, because the pressure difference in each is the same

Click Here to Reveal the Answer

It doesn’t matter the size of the container, its configuration, or from what that container is constructed. It does matter how far below the surface the measurement is taken, and it does matter the density of that material. In this question, in all these cases the distance is 6 inches and the fluid is the same, and therefore, the density is the same. Thus, the pressure is the same.

The answer is E.

About the Author
Joel Don is the community manager for ISA and is an independent content marketing, social media and public relations consultant. Prior to his work in marketing and PR, Joel served as an editor for regional newspapers and national magazines throughout the U.S. He earned a master's degree from the Medill School at Northwestern University with a focus on science, engineering and biomedical marketing communications, and a bachelor of science degree from UC San Diego.

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